<!DOCTYPE html>
<html>
	<head>
		<meta charset="UTF-8">
		<title>标题</title>
		<script type="text/javascript">
			function fun(){
				window.alert("我是警告框");
				document.title="更改标题";
			}
		</script>
	</head>
	<body>
		<input type="button"  value="点我" onclick="fun()"/>
	</body>
</html>
